Recently, early degradation of floor slabs of road bridges such as highway brides has become a problem. More specifically, rainwater, an anti-freezing agent, and the like infiltrate into structures through cracks generated in asphalt pavements and reinforced concrete floor slabs (hereinafter referred to as “RC floor slabs”) and corrode reinforcing bars, thereby decreasing the durability of the structures. Therefore, for the purpose of extending the lifetime of RC floor slabs, in the design specification for road bridges, the Ministry of Land, Infrastructure, Transport and Tourism has stated that a waterproof layer must be provided on RC floor slabs. In June 2001, Nippon Expressway Company Limited (NEXCO) (former Japan Highway Public Corporation) prepared a manual (hereinafter referred to as “JH standards”) regarding a waterproof system for concrete floor slabs. If these standards are satisfied, it is deemed that the floor slab will have a durability of 30 years. These standards are used to strictly evaluate a performance from an initial performance to a long-term performance, such as resistance to opening and closing of cracks, repeated heating/cooling resistance, resistance to paving, salt resistance, and chemical resistance. With regard to these standards, a particularly severe test is the “opening and closing of cracks” in which a fatigue test is performed as many as 4,800,000 times.
At present, there are three types of waterproof layer structures for floor slabs, namely, a sheet structure, a coating structure, and a paving structure. Among these, the paving structure is the least popular because the waterproof performance of the paving structure is poorer than those of the other two structures
Examples of known waterproof coating materials for floor slabs include a urethane urea resin-based waterproof material (PTL 1) and an ether-bond-containing radical-curable resin-based waterproof material (PTL 2).
The urethane urea resin-based waterproof material has an elongation performance that satisfies resistance to the “opening and closing of cracks” and good adhesiveness to a concrete base. However, this urethane urea resin-based waterproof material has problems of troublesome application thereof, for example, a problem in that a large machine is required for application thereof. In contrast, the radical-curable resin-based waterproof material does not require such a large machine and is attractive as a material that can be applied within a short time. However, no radical-curable primers have been developed that have good adhesiveness to a concrete base and resistance to “opening and closing of cracks” as well as a good elongation performance. Accordingly, a radical-curable resin-based waterproof material has yet to be provided as a waterproof system that satisfies resistance to “opening and closing of cracks” and that can be applied within a short time.